The central focus of this proposal explores how to fill a technological gap - the detection of specific A[unreadable] oligomers in living subjects. The development of new techniques for measuring specific A[unreadable] oligomers in living individuals will enable us to investigate how long individuals that are producing A[unreadable]*56, A[unreadable] dimers and A[unreadable] trimers may live before clinically recognizable signs of AD emerge. This project may improve both our understanding of the processes that initiate AD and our ability to diagnose it in its earliest stages, by determining whether specific A[unreadable] oligomers appear early enough in AD to become a target for therapies aimed at preventing the illness altogether. If successful, the work could benefit millions of people in America and the world. Recently, in collaboration with researchers at Rush University, we found that A[unreadable]*56 levels were elevated in many elderly individuals with no cognitive impairment who, presumably, would have developed AD had they lived longer. We also showed that distinct A[unreadable] oligomers were elevated in different phases of the development and progression of AD. Other researchers have missed these intricate patterns in the rise and fall of distinct A[unreadable] oligomers, because they used tests which measure A[unreadable] oligomers in bulk, without distinguishing between distinct species. One test of our hypothesis, that A[unreadable]*56 initiates AD, is to observe the long-term consequences of A[unreadable]*56 in the brain. However, since we cannot monitor A[unreadable]*56 in the brains of living subjects, we will instead measure A[unreadable]*56 in readily accessible test specimens, preferably blood, but also spinal fluid. Using our current immunoblotting methods we can detect A[unreadable]*56 in brain and spinal fluid, but not in blood. This suggests that the levels of A[unreadable]*56 in blood are extremely low, or absent. However, there is indirect evidence in APP transgenic mice that A[unreadable]*56 is present in the blood. In the past few years, researchers in the laboratory of Dr. Srinand Sreevatsan developed DNA aptamers capable of detecting the scrapie isoform of the prion protein in the blood of scrapie-infected sheep, at levels far below the detection threshold of immunoblotting methods. Lately, researchers at the Mayo Clinic led by Dr. Ronald Petersen completed enrollment of nearly 2,000 elderly residents of Rochester, Minnesota, in a longitudinal study of genetic, biomarker, and imaging aspects of aging and very early cognitive problems, and have agreed to make spinal fluid and blood samples available to us. In this Challenge grant application, we propose to collaborate with Dr. Sreevatsan to develop DNA aptamers which detect specific A[unreadable] oligomers, and to use these aptamers to measure distinct A[unreadable] oligomers, including A[unreadable]*56, in the spinal fluid and blood of the Mayo Clinic cohort. PUBLIC HEALTH RELEVANCE: The central focus of this proposal explores how to fill a technological gap - the detection of specific A[unreadable] oligomers in living subjects. The development of new techniques for measuring specific A[unreadable] oligomers in living individuals will enable us to investigate how long individuals that are producing A[unreadable]*56, A[unreadable] dimers and A[unreadable] trimers may live before clinically recognizable signs of AD emerge. This project may improve both our understanding of the processes that initiate AD and our ability to diagnose it in its earliest stages, by determining whether specific A[unreadable] oligomers appear early enough in AD to become a target for therapies aimed at preventing the illness altogether. If successful, the work could benefit millions of people in America and the world.